Note: Opening this as a draft PR to get early feeback. Once we agree on the general direction, I'll continue with these remaining todos:

• Implement for primitive arrays
• Implement for Grid Array Inputs
• Add tests (either e2e or unit tests if applicable)

Description

This adds support for the disableActions option on array fields for disabling various array input capabilities like:

• add – Removes the ability to add new items to the array
• addBefore – Removes the "Add item before"-menu item from the array item menu
• addAfter – Removes the "Add item after"-menu item from the array item menu
• remove – Removes the ability to remove items from the array
• duplicate – Removes the ability to duplicate array items
• copy – Removes the ability to copy items from the array

Usage example:

{
      name: 'someArrayField',
      options: {
        disableActions: ['add', 'duplicate'],
      },
      title: "Array you can't add elements to",
      type: 'array',
      of: [
        {
          type: 'object',
          name: 'something',
          title: 'Something',
          fields: [{name: 'first', type: 'string', title: 'First string'}],
        },
      ],
    }

Things to note:

• These changes are only about UI affordances, and doesn't imply any form of write protection for the actual data
• This only applies to arrays of objects and arrays of primitive values, and not to portable text arrays.
• Disabling add will also implicitly disable addBefore and addAfter, thus disable inserting new items to the array entirely (although items can still be inserted via duplicate).
• There might not be a compelling use case for disabling the ability to copy here(?), but including it for completeness. If all known actions are disabled, the menu items and "add"-affordances will be removed from the UI.
• If we later decide to introduce a new default action, this will appear after upgrading the Studio, and will have to be explicitly disabled.

What to review

Does the feature make sense? Could the API be less confusing?

Testing

• Disable each of the capabilities and check that it works as expected. See the included changes in dev/test-studio/schema/debug/simpleArrayOfObjects.js

Notes for release

• Adds support for the disableActions option on array fields for disabling various array input capabilities

Note: please include the relevant parts from the description of the feature above in the release notes.